Method and device for producing shaped ceramic bodies using setter plates

ABSTRACT

A method and device for producing shaped ceramic bodies, particularly ceramic sheets or multilayer hybrids provided with printed circuit traces, switching elements and/or plated-through holes. The shaped ceramic bodies are initially present as green bodies and also contain organic auxiliary agents, for example as a binder. During sintering and/or removal of the binder from the shaped ceramic bodies, they are compressed between porous setter plates in whose pores a catalytically active substance is introduced, so that the gaseous, organic, bake-out products of the green bodies, these products developing during sintering and/or binder removal, are catalytically converted when escaping through the porous setter plates. The setter plates be provided with separating layers that likewise may contain the catalytically active substance. The method should provide a considerable time savings when sintering and/or removing binder from the shaped ceramic bodies.

This application is a 371 of PCT/DE99/03198 filed Oct. 5, 1999.

FIELD OF THE INVENTION

The present invention relates to a method and a device for producingshaped ceramic bodies.

BACKGROUND INFORMATION

In German Published Patent Application No. 43 09 005 is discussed amethod for producing multilayer hybrids from a plurality of ceramicgreen sheets which contain organic auxiliary agents as binders andsintering aids, and which are provided with printed circuit traces andplated-through holes. The stack of green sheets is pressed together bytwo porous, ceramic setter plates during sintering and removal of thebinder, to ensure the least possible shrinkage and buckling within thegreen sheets. To achieve a simple separation between the setter platesand the multilayer hybrid after the sintering process, the setter platesare provided with a porous separating layer made, for example, ofaluminum oxide which can be applied by slip casting or silk-screenprinting. The organic auxiliary agents in the form of the binder orsintering additive are largely pyrolyzed during the binder removal orsintering, for example, in a hot press under axial pressure, and escapeas organic bake-out products. In this context, the escape takes place,in part, via the porous setter plates or the applied porous separatinglayers which are gas-permeable. Damage to the ceramic sheets may resultfrom burning out the organic auxiliary agents too quickly. Damage mayresult from the diffusion of the broken-up, split-off orpartially-burned organic bake-out products through the setter plates. Itis believed that there is a maximum portion of hydrocarbons in the ovenatmosphere (to remain below the explosion limiting values) determine thespeed for the duration of the binder removal and sintering process.

SUMMARY OF THE INVENTION

An object of an exemplary method of the present invention is to providea method in which the necessary period of time for the sintering andremoval of binder from the shaped ceramic bodies is markedly shortened,without, for example, exceeding the explosion limiting values in theoven atmosphere.

It is believed that the exemplary method of the present invention hasthe advantage that, by introducing a catalytically active substance intothe pores of the porous setter plates and/or into the pores of theporous separating layers, a catalytic conversion of the gaseous bake-outproducts that escape when baking out the green bodies is at leastpartially achieved. The bake-out products are, in one exemplaryembodiment, decomposition products of the organic auxiliary agents andcontain hydrocarbons, among other things.

The escaping bake-out products are, in an exemplary embodiment,converted into less combustible or incombustible gases. In this manner,an exemplary method of the present invention may be used to bake outmore organic auxiliary agents per unit of time than previously, without,for example, the explosion limiting values for hydrocarbons beingreached in the oven atmosphere. It is believed that this results in aconsiderable time savings during the sintering and/or removal of thebinder from the green bodies, and thus to a shortening of the ovencycles, which should mean a marked cost reduction and a substantiallylower need for investment in oven installations.

Moreover, it is believed that catalytically converted, low-molecularoxidation or bake-out products diffuse more quickly through the poroussetter plates and the optionally provided separating layers thanunconverted, high-molecular bake-out products, which may mean a furthertime savings during production. According to one exemplary method and/ordevice of the present invention, installations for the catalyticafterburning of the waste gases carried away from the ceramic greenbodies via the setter plates may be smaller.

According to one exemplary embodiment of the present invention, inaddition to being introduced into the porous setter plates, thecatalytically active substance may also be introduced into the porousseparating layers, which is believed to bring with it advantages fromthe standpoint of process engineering. In an alternative exemplaryembodiment, given an appropriate activity of the introduced,catalytically active substance, it may even be sufficient if thesubstance is only in the porous separating layers, which should lead toa markedly reduced need for these sometimes expensive materials. In thesame way, for some purposes it may be sufficient if the catalyticallyactive substance is merely introduced into the surface area of theporous setter plates or separating layers, for example, by spraying onor impregnating. This may also reduce material costs.

Thus, in one exemplary method according to the present invention,starting materials may be used which, in the course of a thermalafter-treatment of the setter plates and/or the separating layers,respectively, are converted to form metallic, nano-scale particles inthe pores of the setter plates and/or the separating layers.

Another exemplary embodiment involves the selection of a metallic-saltsolution as the starting material for introducing the catalyticallyactive substance. In this exemplary embodiment there may be no unwanted,in particular inorganic, residues remaining in the setter plates and/orseparating layers after the thermal after-treatment.

For faster removal of gaseous bake-out and conversion products, it isbelieved that the setter plates may be provided with additional gasoutlets arranged, in particular, parallel to the surface of the setterplates.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows a ceramic multilayer hybrid composed of a stack ofceramic sheets between two porous setter plates which are separated fromthe stack of sheets by porous separating layers.

DETAILED DESCRIPTION

A shaped ceramic body, which, for example, can be one ceramic sheet, astack of ceramic sheets or a ceramic multilayer hybrid 10 composed ofceramic sheets 1, 2, 3, 4, 5, and which is provided with printed circuittraces, switching elements arid plated-through holes (not shown in theFIGURE), is situated between two porous setter plates 20, 21. The twoporous setter plates 20, 21 may, on the surface on the side facingmultilayer hybrid 10, be provided with porous separating layers 30, 31.Setter plates 20, 21 may be provided with gas outlets 22, e.g. in theform of channels running parallel to the surface of the plates, for morerapid removal of escaping gases. The shaped ceramic body (that is,multilayer hybrid 10) may exist initially as a green body and, inaddition to ceramic components, may also contain organic auxiliaryagents, e.g. in the form of binders, sintering additives, softeners andresidues of solvents.

Setter plates 20, 21 may be made of porous, ceramic materials and may begas-permeable for organic bake-out products which develop during binderremoval and/or sintering of the shaped ceramic bodies. They may bepreferably gas-permeable for low-molecular, gaseous oxidation productssuch as CO, CO₂, H₂O, CH₄, as well as simple hydrocarbons.

The process of sintering and/or removing binder from multilayer hybrid10 is carried out in a hoc press under axial pressure, setter plates 20,21 in particular may prevent sintering shrinkage of multilayer hybrid 10from occurring in the plane of setter plates 20, 21. Since, because oftheir fragility, it is very difficult to handle multilayer hybrids 10from which the binder has been removed, the entire binder removal andsintering process must be carried out in the hot press, although“typically” less than one hour of 11.5 hr. of firing time is necessaryfor the actual sintering under pressure. Essentially, the removal ofbinder from multilayer hybrid 10 by gradual bake-out is carried outduring the remaining time, as a result of which the organic auxiliaryagents are thermally decomposed to a great extent, or volatize,undecomposed, from the green body and are carried away to the outsidethrough the gas-permeable setter plates. Thus, essentially, the time forthe diffusion of the cracked or partially-burned, organic constituentsthrough setter plates 20, 21 is speed-determinate for the binder removalprocess. Since the organic constituents contain a high portion ofhydrocarbon compounds, for reasons of operational safety (protectionagainst explosion), the binder removal process must be carried out sothat the concentration of hydrocarbons in the oven atmosphere alwaysremains below the explosion limiting values.

Porous separating layers 30, 31 simplify the removal of ready-sinteredmultilayer hybrid 10 from setter plates 20, 21. For example, theseparating layers contain essentially ceramic constituents such asaluminum oxide and are preferably applied on setter plates 20, 21 bysilk-screen printing or slip casting. The exemplary method of thepresent invention, however, can also be implemented without separatinglayers 30, 31. Porous separating layers 30, 31, like setter plates 20,21, are gas-permeable for organic bake-out products from the ceramicgreen body.

One aspect of the exemplary method and/or device of the presentinvention is the introduction of a catalytically active substance intosetter plates 20, 21 and/or separating layers 30, 31 prior to beginningthe actual process of sintering and/or removal of binder from the shapedceramic bodies, in order to accelerate the implementation of this binderremoval process.

Catalytically active noble metals such as palladium, rhodium or platinumare believed to be suitable for this purpose. The specific selection ofthe catalytically active substance in the individual case is madeaccording to the type of the organic auxiliary agents and theirquantity, as well as the sintering or binder-removal temperaturesutilized, it always being important and/or necessary to take intoaccount the catalytic activity of the respective material and its costs.The catalytically active substance is used specifically to catalyticallyconvert organic auxiliary agents escaping from the green body duringsintering and/or binder removal. To that end, it is believed to be veryadvantageous if it is located in the pores of the porous materials ofsetter plates 20, 21 and/or of porous separating layers 30, 31, where itis easily available for the escaping gases and can develop a suitablyhigh activity. The catalytically active substance catalytically convertsthe organic hydrocarbon compounds contained in the escaping bake-outproducts by, for example, oxidizing them or converting high-molecular,organic hydrocarbon compounds to form low-molecular hydrocarboncompounds. In particular, it is used for the oxidation of easilycombustible hydrocarbons into incombustible or non-explosive compoundswhich are then removed via the pores in setter plates 20, 21 and/orseparating layers 30, 31, as well as via gas outlets 22.

The catalytically active substance can be introduced into setter plates20, 21 and separating layers 30, 31, respectively, by dipping setterplates 20, 21 into an appropriate metallic-salt solution, or by sprayingthe surface area of setter plates 20, 21 with this solution. In thiscontext, setter plates 20, 21 can already have been provided withseparating layers 30, 31 beforehand, so that the catalytically activesubstance is also introduced into separating layers 30, 31.

By dipping, the catalytically active substance is distributedessentially uniformly within setter plates 20, 21, and optionally withinseparating layers 30, 31, as well. By spraying in particular the side ofthe porous plates facing the ceramic green body, the catalyticallyactive substance is present largely on the surface on setter plates 20,21 and separating layers 30, 31, respectively. Spraying has theadvantage that the quantity of catalytically active material used up isrelatively small, which means lower material costs. On the other hand,because of the distribution on the surface, only a small part of thevolume of setter plates 20, 21 is catalytically active, which means acorrespondingly longer or less complete catalytic conversion of theorganic bake-out products.

In further exemplary embodiments, the catalytically active substance isintroduced only into separating layers 30, 31, for example, bysubsequent spraying. In this case again, it would be important and/ornecessary in the individual case to weigh advantages and disadvantagesfrom the standpoint of process engineering against material costs andthe time savings attained during the binder removal.

To ensure a homogenous and very fine distribution of the catalyticallyactive substance in setter plates 20, 21 and separating layers 30, 31,respectively, or in the corresponding surfaces, they are in an exemplaryembodiment steeped in an aqueous metallic-salt solution containing atleast one of the metallic salts PtCl₆, PdCl₂, RhCl₃, platinum acetate,rhodium acetate or palladium acetate. The concentration of thecatalytically active substance in this metallic-salt solution may bebetween 0.1 g/l to 30 g/l. Concentrations of 1 g/l to 15 g/l have turnedout to be particularly advantageous. In this case, in a setter plate 20weighing 1 kg, when using a platinum solution containing 10 g ofplatinum to 1 liter of solution, approximately 0.6 g of platinum isintroduced into setter plate 20. When using a solution containing 6 g ofpalladium to 1 liter of solution, approximately 0.4 g of palladium isintroduced per plate.

After setter plates 20, 21 have been sprayed or dipped, a thermalafter-treatment of setter plates 20, 21 with the introducedcatalytically active substance is expediently carried out. Depending onthe size of the plates, the type of metal introduced and themetallic-salt solution employed, this after-treatment lasts from 30minutes to 5 hours at a temperature of 100° C. to 700° C. This may becarried out in a gas atmosphere, such as air or nitrogen, which does notoxidize the catalytically active substance. However, when working with afew catalytically active materials which can be oxidized relativelyeasily, in order to avoid oxidation, it is believed to be best if workis carried out in a reductive gas atmosphere. For example, in the caseof platinum, rhodium and palladium, it is sufficient if the thermalafter-treatment is carried out at 500° C. over 2 hr. in air.

The use of organic metallic compounds, such as the acetates indicated,is particularly recommendable for applications in which no residues ofthe introduced metallic-salt solution are to remain in setter plates 20,21 and separating layers 30, 31 after the thermal after-treatment, sincethese compounds thermally decompose in a substantially residue-freemanner during the thermal after-treatment.

In another exemplary embodiment, the catalytically active substance ispresent in the form of uniformly distributed, nano-scale, metalliccolloids of, for example, platinum, rhodium or palladium in the pores ofthe porous setter plates and separating layers, respectively. It isbelieved that the size of these colloids is advantageously between 3 nmand 100 nm, in order to attain the highest possible specific surfaceareas, and thus an effective seeding of setter plates 20, 21 or ofseparating layers 30, 31.

What is claimed is:
 1. A method for producing a formed body, the formedbody including at least one of a formed ceramic body, a ceramic sheetand a multilayer hybrid, the formed body having at least one of aprinted circuit trace, a switching element and a plated throughhole, themethod comprising the steps of: disposing a plurality of green bodiescontaining an organic auxiliary agent between porous setter plates,through which a gaseous, organic, bake-out product escapes from theplurality of green bodies developed during at least one of a sinteringoperation and a binder removal operation, the step of disposing beingperformed during at least one of the sintering operation and the binderremoval operation; and introducing a catalytically active substance intopores of at least one of the porous setter plates, the catalyticallyactive substance converting the gaseous, organic, bake-out product intorelatively less combustible compounds.
 2. The method of claim 1, whereinthe catalytically active substance oxidizes an organic hydrocarboncompound.
 3. The method of claim 1, wherein the catalytically activesubstance converts a high-molecular, organic hydrocarbon compound to alow-molecular, organic hydrocarbon compound.
 4. The method of claim 1,wherein the catalytically active substance includes at least one ofplatinum, palladium and rhodium.
 5. The method of claim 1, wherein thecatalytically active substance is in a form of colloids, the colloidshaving sizes of 3 nm to 100 nm.
 6. The method of claim 1, wherein theformed body is a ceramic multilayer hybrid, and the plurality of greenbodies includes a stack of a plurality of green sheets arranged in ajustified manner one upon the other and provided with at least one ofthe printed circuit trace, the switching element and the plated-throughhole.
 7. The method of claim 1, wherein the catalytically activesubstance is introduced into the pores of the at least one of the poroussetter plates in the step of introducing.
 8. A device for producing aformed body, the formed body including at least one of a formed ceramicbody, a ceramic sheet and a multilayer hybrid, the formed body having atleast one of a printed circuit trace, a switching element and a platedthroughhole, the device comprising: porous setter plates, a plurality ofgreen bodies containing an organic auxiliary agent being disposablebetween the porous setter plates, through which a gaseous, organic,bake-out product escapes from the plurality of green bodies developedduring at least one of a sintering operation and a binder removaloperation; wherein: a catalytically active substance is introduced intopores of at least one of the porous setter plates, the catalyticallyactive substance converting the gaseous hydrocarbons into relativelyless combustible compounds; and the porous setter plates include gasoutlets.
 9. A method for producing a formed body, the formed bodyincluding at least one of a formed ceramic body, a ceramic sheet and amultilayer hybrid, the formed body having at least one of a printedcircuit trace, a switching element and a plated throughhole, the methodcomprising the steps of: disposing a plurality of green bodiescontaining an organic auxiliary agent between porous setter plates,through which gaseous hydrocarbons escape from the plurality of greenbodies developed during at least one of a sintering operation and abinder removal operation, the step of disposing being performed duringat least one of the sintering operation and the binder removaloperation; and introducing a catalytically active substance into poresof at least one of the porous setter plates, the catalytically activesubstance converting the gaseous hydrocarbons into relatively lesscombustible compounds.
 10. The method according to claim 9, wherein thecatalytically active substance oxidizes the gaseous hydrocarbon.
 11. Themethod according to claim 9, wherein the catalytically active substanceconverts the gaseous hydrocarbon to a relatively lower-molecular weighthydrocarbon.
 12. The method according to claim 9, wherein thecatalytically active substance is a metallic-salt solution.
 13. Themethod according to claim 9, wherein the catalytically active substanceincludes at least one of platinum, palladium and rhodium.
 14. A methodfor producing a formed body, the formed body including at least one of aformed ceramic body, a ceramic sheet and a multilayer hybrid, the formedbody having at least one of a printed circuit trace, a switching elementand a plated throughhole, the method comprising the steps of: disposinga plurality of green bodies containing an organic auxiliary agentbetween porous setter plates, through which gaseous hydrocarbons escapefrom the plurality of green bodies developed during at least one of asintering operation and a binder removal operation, the step ofdisposing being performed during at least one of the sintering operationand the binder removal operation; and spraying a catalytically activesubstance onto the porous setter plates, the catalytically activesubstance converting the gaseous hydrocarbons into relatively lesscombustible compounds.
 15. The method according to claim 14, wherein thecatalytically active substance is a metallic-salt solution.
 16. Themethod according to claim 14, wherein the catalytically active substanceconverts the gaseous hydrocarbon to a relatively lower-molecular weighthydrocarbon.
 17. The method according to claim 14, wherein thecatalytically active substance includes at least one of platinum,palladium and rhodium.
 18. A method for producing a formed body, theformed body including at least one of a formed ceramic body, a ceramicsheet and a multilayer hybrid, the formed body having at least one of aprinted circuit trace, a switching element and a plated throughhole, themethod comprising the steps of: disposing at least one porous separatinglayer on inner surfaces of porous setter plates; disposing a pluralityof green bodies containing an organic auxiliary agent between the poroussetter plates, through which a gaseous, organic, bake-out productescapes from the plurality of green bodies developed during at least oneof a sintering operation and a binder removal operation, the step ofdisposing being performed during at least one of the sintering operationand the binder removal operation; and introducing a catalytically activesubstance into pores of at least one porous separating layer of theporous setter plates, the catalytically active substance converting thegaseous, organic, bake-out product into relatively less combustiblecompounds.
 19. The method of claim 18, wherein the catalytically activesubstance is introduced into the pores of the at least one porousseparating layer in the step of introducing.
 20. The method of claim 18,wherein the catalytically active substance is also introduced into poresof at least one of the porous setter plates.
 21. The method of claim 18,wherein the catalytically active substance is at least one ofintroduced: (i) into a surface area of at least one of the porous setterplates and the at least one porous separating a layer; and (ii)uniformly inside at least one of the porous setter plates and the atleast one porous separating layer.
 22. The method of claim 18, furthercomprising the step of thermally treating at least one of (i) at leastone of the porous setter plates and (ii) the at least one porousseparating layer, after the step of introducing the catalytically activesubstance; wherein the step of introducing the catalytically activesubstance is performed by at least one of steeping in a solution andspraying with the solution, the solution containing the catalyticallyactive substance.
 23. The method of claim 22, wherein the solution is ametallic-salt solution.
 24. The method of claim 23, wherein themetallic-salt solution is an aqueous solution including at least one ofPtCl6, PdCl2, RhCl3, platinum acetate, palladium acetate and rhodiumacetate.
 25. The method of claim 22, wherein the solution includes thecatalytically active substance in a concentration of 0.1 g/l to 30 g/l.26. The method of claim 22, wherein the step of thermally treating isperformed in a gas atmosphere that at least one of (i) does not oxidizethe catalytically active substance and (ii) reduces the catalyticallyactive substance.
 27. The method of claim 22, wherein the step ofthermally treating is performed over a time period of 30 minutes to 5hours at a temperature of 100 degrees Celsius to 700 degrees Celsius.28. A device for producing a formed body, the formed body including atleast one of a formed ceramic body, a ceramic sheet and a multilayerhybrid, the formed body having at least one of a printed circuit trace,a switching element and a plated throughhole, the device comprising:porous setter plates having at least one porous separating layerdisposed between them, a plurality of green bodies containing an organicauxiliary agent being disposable between the porous setter plates,through which a gaseous, organic, bake-out product escapes from theplurality of green bodies developed during at least one of a sinteringoperation and a binder removal operation; wherein: a catalyticallyactive substance is introduced into pores of at least one porousseparating layer of the porous setter plates, the catalytically activesubstance converting the gaseous hydrocarbons into relatively lesscombustible compounds; and the porous setter plates include gas outlets.29. The device of claim 28, wherein the catalytically active substanceis introduced to a porous arrangement, the porous arrangement includingone of (i) at least two of the porous setter plates and (ii) at leasttwo of the porous separating layers, the porous arrangement being forcompressing the plurality of green bodies during the at least one of thesintering operation and the binder removal operation.
 30. The device ofclaim 29, wherein the porous arrangement is permeable for at least oneof a low-molecular, gaseous, oxidation product CO, CO2, H2O, CH4 and ahydrocarbon.
 31. A method for producing a formed body, the formed bodyincluding at least one of a formed ceramic body, a ceramic sheet and amultilayer hybrid, the formed body having at least one of a printedcircuit trace, a switching element and a plated throughhole, the methodcomprising the steps of: disposing at least one porous separating layeron inner surfaces of porous setter plates; disposing a plurality ofgreen bodies containing an organic auxiliary agent between the poroussetter plates, through which gaseous hydrocarbons escape from theplurality of green bodies developed during at least one of a sinteringoperation and a binder removal operation, the step of disposing beingperformed during at least one of the sintering operation and the binderremoval operation; and introducing a catalytically active substance intopores of at least one porous separating layer of the porous setterplates, the catalytically active substance converting the gaseoushydrocarbons into relatively less combustible compounds.
 32. The methodaccording to claim 31, wherein the catalytically active substance isintroduced in the introducing step by spraying the at least one of theporous setter plates and porous separating layer of the porous setterplates.
 33. The method according to claim 31, wherein the catalyticallyactive substance is introduced in the introducing step by steeping theat least one of the porous setter plates and porous separating layer ofthe porous setter plates.
 34. A method for producing a formed body, theformed body including at least one of a formed ceramic body, a ceramicsheet and a multilayer hybrid, the formed body having at least one of aprinted circuit trace, a switching element and a plated throughhole, themethod comprising the steps of: disposing at least at least one porousseparating layer on inner surfaces of porous setter plates; disposing aplurality of green bodies containing an organic auxiliary agent betweenthe porous setter plates, through which gaseous hydrocarbons escape fromthe plurality of green bodies developed during at least one of asintering operation and a binder removal operation, the step ofdisposing being performed during at least one of the sintering operationand the binder removal operation; and spraying a catalytically activesubstance onto at least one porous separating layer of the porous setterplates, the catalytically active substance converting the gaseoushydrocarbons into relatively less combustible compounds.